In layman’s terms, we can call any heart development defect congenital heart disease if it is carried at birth. Some of these defects are caused by abnormal development of the cardiovascular system during fetal life, while others are hemodynamic abnormalities due to failure to close channels that were normal during fetal life but should have closed automatically after birth. According to the direction of blood flow, congenital heart disease can be classified as left-to-right shunt preconditioning, right-to-left shunt preconditioning, obstructive preconditioning, and other complex preconditioning. The symptoms vary according to the direction of blood shunt; the manifestations of the same disease may change with age. Ventricular septal defect, atrial septal defect, and patent ductus arteriosus are the three most common types of left-to-right shunt precardiac disease, and their disease manifestations are related to the size of the defect and the shunt flow. Small shunts (mild disease) can be asymptomatic, and a heart murmur can be detected by the physician during physical examination. If the shunt flow is high, there may be a decrease in milk consumption, straining or stopping of milk consumption, easy choking, shortness of breath, slow weight gain, and easy occurrence of respiratory infections or recurrent pneumonia. All of these manifestations are symptoms of left heart insufficiency and require early surgical treatment. If the fractional flow is between the two, it may not be easily detected and only appears to be lower in weight than normal children, but normal in height. It may not affect exercise capacity. Generally speaking, right-to-left shunt preconditioning is a complex type of preconditioning that is difficult to treat surgically. Tetralogy of Fallot is one of the more common right-to-left shunt precardiac diseases, and its incidence is lower than that of ventricular septal defect, atrial septal defect, and patent ductus arteriosus. The most characteristic feature of right-to-left shunt preconditioning is cyanosis, and some people used to think that all children with preconditioning would have “perioral cyanosis,” which is actually a misconception that the manifestation of right-to-left shunt preconditioning is the manifestation of all preconditioning. Cyanosis is not usually present in newborn children with tetralogy of Fallot, but usually develops gradually with age. It is important to mention here that if cyanosis is found at birth, it is usually caused by other complex precocious diseases. As a result of systemic hypoxia, the body develops further changes with age – vascular hyperplasia. Pestle-shaped fingers (toes) on the hands and feet, and eyes that can be covered with blood, are all signs of vascular hyperplasia. The doctor’s main concern is the pulmonary collateral vessels, which are very important for the patient’s recovery after surgery. Squatting after activity is a common manifestation of tetralogy of Fallot. There is also a group of obstructive precordial disease, which usually has local obstruction, e.g., pulmonary valve stenosis. The pre-infarct is characterized by increased pressure and compensatory hypertrophy of the myocardium; the post-infarct vessels can become dilated due to blood flow impact. These patients do not necessarily have clinical symptoms in the early stages, but later they may show signs of right heart insufficiency, such as decreased activity tolerance, shortness of breath, enlarged liver and spleen, and possible arrhythmias in the presence of myocardial hypertrophy. Other complex precordial diseases include transposition of the great arteries and pulmonary atresia, etc. Because of the low incidence and the complexity of the disease, the choice of surgical methods is beyond the grasp of ordinary patients, so we will not discuss them here. Babies with mild cases of precordial disease can be treated as normal children: they can play normal sports, receive vaccinations, and go to school for physical education classes. It is important to note that these children should visit the hospital for annual electrocardiograms and cardiac ultrasounds as a follow-up of their condition. If the condition is not a mild congenital heart disease and the previously mentioned manifestations of the condition are present, it is important to have surgical treatment as soon as possible, or at least to have the condition evaluated by a doctor who can perform congenital heart surgery.